Heery and Cope: Co-occurrence of bycatch and target species in the groundfish trawl fishery 
47 
lection of such information over a spatial scale that 
matches the fishery would be challenging. 
If the same species clusters continue to be identified 
for each departure port as more data become available, 
they may provide evidence to support a more localized 
approach in the data analyses that support fishery 
management. Currently, bycatch data analyses in the 
bottom trawl fishery are structured to support manag- 
ers who are responsible for implementing management 
measures over a vast area, from northern Washington 
to southern California (Bellman and Heery, 2013). The 
measures developed by managers have historically in- 
cluded a combination of trip limits, area closures, gear 
restrictions, and other approaches (King et ah, 2004, 
Bellman et ah, 2005; Branch, 2006). Regulations are 
often developed through the use of fishery data that 
have been stratified into a series of smaller manage- 
ment areas. However, even at this level, the measures 
put in place may be formed on the basis of fishery in- 
formation from an area spanning hundreds of kilome- 
ters and may therefore affect vessels from a variety of 
different ports (Bellman and Heery, 2013). 
This is not to say that large-scale management is 
ineffective. Fishery managers often rely on bycatch ra- 
tios to set bimonthly trip limits and closures of a given 
area to fishing. Even if species assemblages containing 
rebuilding and other nontarget species are not evident 
at the scale being used by managers, the bycatch ratios 
calculated for these areas should still provide an ac- 
curate large-scale representation of bycatch. However, 
more specific measures that relate bycatch of rebuild- 
ing species to catch or landings of a smaller subset 
of target species may be more relevant if developed 
through the use of fishery data specific to each port. 
For instance, bycatch of Darkblotched Rockfish and Pa- 
cific Ocean Perch may be more accurately estimated 
for northern ports by using catch of other deepwater 
rockfish species as a proxy for fishing effort. However, 
in other neighboring ports, this relationship with other 
deepwater rockfish species may not be relevant. For 
this approach to be effective, more data would need to 
be collected onboard fishing vessels so that potential 
species assemblages noted in this analysis can be con- 
firmed and monitored over time. More data have be- 
come available since the 2011 implementation of the 
catch shares program (Toft et al., 2011), which required 
100% observer coverage. Localized species assemblages 
identified from this new, more comprehensive data set, 
by using the methods presented here, could provide 
considerable insight to fishery managers as they con- 
tinue to develop measures aimed at reducing bycatch 
of rebuilding species. 
Conclusions 
Data from the West Coast Groundfish Observer Pro- 
gram provided valuable insight into whether there were 
associations between target and nontarget groundfish 
species harvested commercially in the west coast de- 
mersal trawl fishery. Although many target species 
formed identifiable clusters, most rebuilding species 
did not form groupings. This characteristic of rebuild- 
ing species may complicate the use of bycatch ratios 
for fishery management purposes. We used a simula- 
tion approach to separate the effect of low rates of oc- 
currence of rebuilding species from the actual tendency 
of these species to group with target species in cluster 
analyses. Our findings indicate that, although bycatch 
relationships between target and rebuilding species of- 
fer low predictive potential when coastwide data are 
used collectively; such relationships may be useful for 
predicting bycatch for specific port groups or for esti- 
mating bycatch amounts on tows when rare bycatch 
events do actually occur. 
Acknowledgments 
We are grateful to the fishery observers who have com- 
piled tremendously valuable data through hard work 
and dedication. We also thank observer program staff 
for their support, M. Bellman for her central role in the 
processing of the data used in our study and for provid- 
ing the map figure, and J. Majewski for the comments 
and insight she provided for the manuscript. 
Literature cited 
Alverson, D. L., M. H. Freeberg, S. A. Murawski, and J. G. 
Pope. 
1994. A global assessment of fisheries bycatch and dis- 
cards. FAO Fish. Tech. Pap. 339, 233 p. FAO, Rome. 
Beddington, J. R., D. J. Agnew, and C. W. Clark. 
2007. Current problems in the management of marine 
fisheries. Science 316:1713-1716. 
Bellman, M. A., S. A. Heppell, and C. Goldfinger. 
2005. Evaluation of a US west coast groundfish habi- 
tat conservation regulation via analysis of spatial and 
temporal patterns of trawl fishing effort. Can. J. Fish. 
Aquat. Sci. 62:2886-2900. 
Bellman, M. A., and E. Heery. 
2013. Discarding and fishing mortality trends in the U.S. 
west coast groundfish demersal trawl fishery. Fish. 
Res. 147:115-126. 
Branch, T. A. 
2006. Discards and revenues in multispecies groundfish 
trawl fisheries managed by trip limits on the U.S. West 
Coast and by ITQs in British Columbia. Bull. Mar. Sci. 
78:669-690. 
Clark, L. A., and D. Pregibon. 
1992. Tree-based models. In Statistical models in S (J. 
M. Chambers and T. J. Hastie, eds.), p. 377-419. Wad- 
sworth and Brooks, Pacific Grove, CA. 
Collie, J. S., G. A. Escanero, and P. C. Valentine. 
1997. Effects of bottom fishing on the benthic megafau- 
na of George’s Bank. Mar. Ecol. Prog. Ser. 155:159-172. 
Cope, J. M., and M. A. Haltuch. 
2012. Temporal and spatial summer groundfish assem- 
